Piston-operated tensioning apparatuses or devices with adjusting means are very popular and are especially used for timing chain drives in internal combustion engines. In this connection, the housing forms, together with a hollow cylindrical tensioning piston, a pressure chamber in the piston bore of the housing, said chamber commonly being filled with a hydraulic means and being provided with a pressure spring to preload the tensioning piston. In many cases, such tensioning devices comprise adjusting means in the form of locking mechanisms defining a blocking and sliding direction for the tensioning piston, thereby preventing the tensioning piston to move into the housing too deeply by means of a stopper, yet allowing the working stroke of the tensioning piston to be adjustable.
Such a tensioning apparatus with conventional locking mechanism is known from DE 100 14 700 A1 in which the tensioning piston includes a saw tooth profile into which a ratchet block engages through a window opening of the housing. In said tensioning apparatus, the free working stroke of the tensioning piston is limited by the axial freedom of motion of the ratchet block in said housing window.
A generic tensioning apparatus or device is known from DE 196 80 418 C1. Here, the tensioning piston of said hydraulic tensioner comprises multiple circumferential axially spaced-apart snap-in grooves. A locking bracket is slipped onto the tensioning piston and initially engages into the uppermost snap-in groove of said tensioning piston by means of a ring-shaped section of the locking bracket. For adjusting or regulating said ring-shaped spring clip the housing is provided with a lower chamfered stop face as well as an upper stop ring embedded in the inner circumference of the housing bore. There is ample operating range therebetween to allow the tensioning device to deploy its damping effect. To form the stoppers, the locking bracket is provided with a U-shaped section and with two end legs radially extending outwards from said ring-shaped clamping section and moving in the working stroke of the tensioning piston in corresponding housing windows between the lower stopper and the upper stop ring. When the working stroke of the tensioning piston is adjusted or regulated, the locking bracket abuts at the upper stop ring, and the tensioning piston advancing further due to wear-stretching of the chain radially widens or spreads-apart the ring-shaped section of the locking bracket and pushes, in case of sufficient advancing movement, said locking bracket into the next locking profile groove. To spread apart or widen the ring-shaped section of the locking bracket, both arch-shaped clamping sections thereof are bent apart in the region of the U-shaped section. In order to ensure a reversible, spring-elastic bending, the diameter of the round wire used for the locking bracket must not exceed a thickness depending on the diameter of the tensioning piston and the widening of the ring-shaped clamping section. If the ring-shaped section of the locking bracket abuts against the lower chamfered stop face during a retraction movement of the tensioning piston, the ring-shaped section of the locking bracket is pressed into the locking groove and the retraction movement of the tensioning piston into the housing is blocked. The clamping effect of the locking bracket for blocking the retraction movement can be improved by larger round wire diameters.
Tensioning apparatuses or devices including adjusting or regulating means for limiting the retraction movement of a tensioning piston and simultaneously defining the free working stroke of said tensioning piston are very popular in technology in a variety of concepts and embodiments and proved successful when in action. Unfortunately, adjusting such tensioning devices generally requires relatively complex structures and definite adaptations to the functions thereof as well as individual manufacture of the required components.
The tensioning devices with adjusting means as known in technology are available in a variety of concepts with the embodiments directed to the corresponding case of application. However, due to the progressive technical development, also those products that have already been well-established in technology underlie the constant pressure to come up with innovations in order to improve existing designs. Considering the increasing cost pressure in combination with huge quantities particularly in the automotive industry, there is a general continuous need for optimization and the attempt to reduce costs by synergy effects.